1. Field
The disclosed subject matter relates to a vehicle light which employs a semiconductor light emitting device as a light source.
2. Description of the Related Art
In recent years, the output power of a semiconductor light emitting device such as an LED has increased, and the luminance thereof has increased accordingly. With the increase in the luminance, the development of an LED and the like used as a light source for a vehicle light is continuously in progress.
Japanese Patent Application Laid-Open No. 2005-276805 discloses a vehicle light which employs a semiconductor light emitting device such as an LED, for example, as a light source. An example of the configuration of such a vehicle light is shown in FIG. 1.
In FIG. 1, a vehicle light 1 of the conventional example is constituted as a headlight for an automobile and is configured to include at least one optical unit 2.
The optical unit 2 may include: a light source 3; a first reflector 4; a second reflector 5; a third reflector 6; a projection lens 7; and a shutter 8.
The light source 3 is composed of at least one LED 3a mounted on a substrate (not shown). Here, the LED 3a is disposed so as to emit light in an upward direction. In this configuration, a driving voltage is applied to the LED 3a from an exterior power source to drive it and realize an emission of light.
It should be noted that examples of the semiconductor light emitting device employed in the light source 3 may include, in addition to an LED, a semiconductor laser device, etc.
The first reflector 4 is formed from an elliptic reflection surface having a fist focus F1 located in the vicinity of the light source 3 and a second focus F2 located in the vicinity of a rear side focus of the projection lens 7.
The second reflector 5 is formed from an elliptic reflection surface having a fist focus located in the vicinity of the light source 3 and a second focus F3 located on a line connecting the light source 3 and the rear side focus of the projection lens 7.
The third reflector 6 is formed from an elliptic reflection surface having a fist focus located in the vicinity of the second focus of the second reflector 5 and a second focus located in the vicinity of the rear side focus of the projection lens 7. Alternatively, the third reflector 6 can be formed from a parabolic reflection surface having a focus in the vicinity of the second focus of the second reflector 5 and having an optical axis extending horizontally forward.
The projection lens 7 is composed of a convex lens. The light that has been reflected by the first reflector 4 or the third reflector 6 and then which converges in the vicinity of the rear side focus of the projection lens 7 is projected forward through the projection lens 7 to be substantially parallel light.
The shutter 8 is placed in the vicinity of the rear side focus of the projection lens 7, and an upper edge 8a of the shutter 8 forms a cut-off for shaping, for example, a passing light distribution beam.
In the vehicle light 1 having such a configuration, when power is supplied to the LED 3a of the light source 3 of the optical unit 2, the LED 3a is driven to emit light. Then, part of the light emitted from the LED 3a is incident on the projection lens 7 either directly or indirectly after being reflected by the first reflector 4. That total light is then projected forward.
Furthermore, the light incident on the second reflector 5 is reflected thereby and is directed toward the third reflector 6. Then, the light is reflected by the third reflector 6, and the reflected light is incident on the projection lens 7. As a result, the light is projected forward through the projection lens 7.
At this time, the light converging toward the rear side focus of the projection lens 7 is partially blocked by the shutter 8, and a cut-off is formed by the upper edge 8a thereof. The light having the thus-shaped light distribution pattern (for example, a passing beam light distribution) is projected forward.
Generally, an LED for use in such a vehicle light 1 is often encapsulated with a resin such as a silicon resin. Since such a silicon resin has a certain degree of hygroscopicity, the silicon resin may deteriorate due to absorption of moisture during long-term use. In this case, the optical characteristics of the LED as a whole may be changed. That is, the light emitting quality may deteriorate.
For example, in reliability experiments for an LED formed of GaAlAs as a base material, the luminous intensity of emitted light was 106.6% of the original intensity after the LED was energized for 1,000 hours at room temperature (25° C.), 106.3% after the LED was energized for 1,000 hours at high temperature (85° C.), and 96.6% after the LED was energized for 1,000 hours at low temperature (−40° C.). However, after the LED was energized for 1,000 hours at high temperature (80° C.) and high humidity (85%), the luminous intensity of emitted light was 84.7%. Thus, it was found that deterioration due to humidity was significant.
Furthermore, in the case of an LED formed of phosphor-containing GaN as a base material, the luminous intensity of emitted light was 89.6% after the LED was energized for 1,000 hours at high temperature (60° C.) and high humidity (90%). Similarly, it was found that the deterioration due to humidity was significant.
Such a problem may occur not only when a light source is a resin-encapsulated LED but also when a light source is selected from one of other types of semiconductor light emitting devices such as semiconductor laser devices, etc.
Examples of the reflectors 4, 5, and 6 include reflectors having a reflection surface coated with, for example, vapor deposited silver. When such reflectors are employed, the surface thereof may oxidize or sulphidize during long-term use. In particular, when the surface is sulphidized, the appearance color may change which can result in a reduction in reflectivity.